For the intra-body communication system, ECMA-401 is developed as the standard specification (Non-Patent Literature 1). In the association procedure defined in this specification, a terminal (Talker) intended to initiate association transmits Association Request1, and a terminal (Listener) serving as an association peer, when receiving it, transmits Association Response1 as reply to the terminal (Talker). The terminal (Talker), when receiving Association Response1, transmits Association Request2 for association verification to the terminal (Listener), the terminal (Listener), when receiving it, transmits Association Response2 as an acknowledgment to the terminal (Talker), and then the association procedure is completed.
In this standard specification, five rates are defined as the sampling rate of the physical layer, each of which is FDC0, 1, 2, 3, and 4. In addition, as the timing rule, a superframe called Time Segment is composed of eight time slots (TDSs). It is defined that each of the frames (Association Request1, Association Request2, Association Response1, and Association Response2) used in the association procedure is performed at the sampling rate called FDC2, and each frame is transmitted in one TDS.
The terminal (Talker) transmits Association Request1 in one TDS selected among TDS0 to 3, on the basis of timing generated by the terminal itself. The TDS number (any one of 0 to 3) transmitted by the terminal (Talker) is described in Association Request1. The terminal (Listener), when receiving Association Request1, can synchronize with the slot timing of the terminal (Talker) on the basis of the described TDS number. Then, the terminal (Listener) transmits Association Response1 to the terminal (Talker) at the timing of +4TDS, which is defined in the specification.
This is applied similarly to Association Request2 and Association Response 2, that is, it is defined that transmission can performed at the timing of +4TDS of the frame received immediately before.